This invention relates generally to a method and apparatus for controlling combustion timing of an internal combustion engine and, more particularly, to a method and apparatus for controlling cylinder-to-cylinder timing variations caused by crankshaft deformation.
Control of combustion timing of cylinders in an internal combustion engine significantly affects performance characteristics of the engine. The timing events which initiate combustion control the fuel efficiency, gaseous emissions formation, and internal loads generated in each cylinder.
Many methods and systems exist which determine the engine crankshaft position, thus providing the information needed to control delivery timing to desired values. For example, in U.S. Pat. No. 5,860,406, Schmidt et al. disclose an apparatus and method which monitors the rotation of a crankshaft, monitors the rotation of a camshaft, and responsively determines engine timing. The timing information is then used to initiate fuel injection into cylinders at the desired time. Other examples of methods and systems which determine engine timing exist, many of which determine an angular position of the crankshaft as an integral part of the method.
Multiple cylinder engines, in particular larger or high performance engines, generate tremendous amounts of torque under certain operating conditions. This torque is centered about the crankshaft, which operates as a power transfer device between the pistons and the drive train. Although crankshafts are designed to withstand the stresses associated with this torque, some degree of deformation of the crankshaft takes place. The deformation of the crankshaft reflects back to the positions of the pistons with respect to each other. This change in individual piston position causes timing variations relevant to individual cylinders. More specifically, cylinder-to-cylinder timing is adversely affected.
The timing methods in use today can monitor and control overall engine timing, but cannot account for cylinder-to-cylinder delivery timing variations caused by crankshaft deformations.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention a method for controlling timing of an internal combustion engine having a piston located in a cylinder is disclosed. The method includes the steps of determining a first angular position of a crankshaft at a first location along a longitudinal axis of the crankshaft, determining a second angular position of the crankshaft at a second location along the longitudinal axis, determining a level of deformation of the crankshaft as a function of a difference between the first and second angular positions, determining an actual position of the piston as a function of the crankshaft deformation, comparing the actual piston position to a desired piston position, and controlling timing of an event to initiate combustion in the cylinder as a function of a difference between the actual and desired piston positions.
In another aspect of the present invention an apparatus for controlling timing of an internal combustion engine having a piston located in a cylinder is disclosed. The apparatus includes a first crankshaft angular position determiner located to determine an angular position at a first location along a longitudinal axis of a crankshaft, a second crankshaft angular position determiner located to determine an angular position at a second location along the longitudinal axis, and a controller for determining a level of deformation of the crankshaft as a function of a difference between the first and second angular positions, determining an actual position of the piston as a function of the crankshaft deformation, comparing the actual piston position to a desired piston position, and controlling timing of an event to initiate combustion in the cylinder as a function of a difference between the actual and desired piston positions.